Deviation analysis of plan verification results of 260 volumetric modulated arc therapy plans / 中华放射肿瘤学杂志

ABSTRACT

Objective To investigate the γ pass rate and contributing factors by summarizing the plan verification results of 260 volumetric modulated arc therapy (VMAT) plans.Methods From 2010 to 2012,two different detector arrays (MapCheck2,Sun,Nuclear,USA ; Delta4 ScandiDos,Swenden) were used for plan verification in 260 patients.The measured dose distributions were compared with the calculation results of treatment planning system using γ pass rate (Pγ ≤ 1 for 2％/2 mm,3％/3 mm and 5％/3 mm,threshold 10％).And the results were put under independent-samples t test.The impact of multi-leaf collimator (MLC) on the γ pass rate (3％/3 mm) was analyzed.Results The average γ pass rates of 2％/2 mm,3％/3 mm and 5％/3 mm of 260 VMAT plans were 91.7％,98.5％ and 99.7％,respectively.Among 260 VMAT plans,3 VMAT plans (1.2％ of the total) failed to meet the clinical acceptable pass rate and needed to be redesigned or re-optimized.The γ pass rate of 2％/2 mm was slightly different between two measurement devices (90.0％ vs 93.5％,P =0.000),while the γ pass rate of 3％/3 mm showed no significant difference between two measurement devices and two accelerators (98.5％ vs 98.5％,P =0.926 and 98.5％ vs 98.6％,P =0.670).The γ pass rate (3％/3 mm) of the treatment plan before MLC calibration was 61.1％,compared to 94.1％ after calibration.Conclusions Most dose verification results of treatment plans can meet the clinical requirement.Gantry rotation may influence the γ pass rate of VMAT dose verification under stricter pass rate standard (2％/2 mm).MLC calibration is essential for VMAT.